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How Emerald Ash Borers Destroy Ash Trees

  • It is actually the larvae (caterpillar stage), not the adults that destroy ash trees. After hatching, the larvae bore directly into the bark and begin feeding just under the bark in the phloem (food conducting tissue) of the tree creating s-shaped galleries.
  • This is when the damage occurs because the flow of nutrients in the tree is disrupted by the larval feeding. During winter, the larvae stay under the bark of ash trees and pupate in early spring (mid-April) with adult emergence in late May to the end of June.
  • The adults feed on ash foliage for two to four weeks which is characterized by a notched feeding pattern on the leaves. This stage is not damaging to the trees.
  • From the end of June until the end of August, the adult female lays up to 300 individual eggs (average 75) on the bark of ash trees or in bark crevices.
  • Emerald ash borers have a one to two-year life cycle depending on infestation levels and climate conditions.
  • It takes one to five years of infestation to kill the tree. At low levels the Emerald Ash Borer is hard to detect, but after the population builds, ash trees start dying. In places like Michigan where the population of Emerald Ash Borer went undetected for many years, millions of ash trees have been killed by this invasive species.

Image of a destroyed ash tree